In Graham v. Florida, the Supreme Court held that the Eighth Amendment prohibits imposing a sentence of life in prison without the possibility of release for nonhomicide crimes if the perpetrator was under the age of eighteen at the time of his offense. In so holding, Justice Kennedy cited foreign and international law to confirm the Court’s independent judgment. In his dissent, Justice Thomas recited now-familiar objections to the Court’s reliance on these sources. Those objections are grounded in his originalist jurisprudence. In this short invited essay, which expands on prior work, we argue that Justice Thomas should abandon these objections. That is because the Eighth Amendment’s prohibition on cruel and unusual punishment incorporates objective moral constraints rather than common public views held by Americans in 1792. While we acknowledge that courts asked to determine these objective constraints face a significant epistemic challenge. However, we suggest that the most reliable approach lies not with historical inquiry but with a method akin to that endorsed by Jürgen Habermas’s discourse ethics. In particular, to the extent that foreign, transnational, and international law addressing the cruelty of various punishment practices is the result of an inclusive process of open debate among those with an interest in the answer, we think that domestic courts are well-advised to follow Justice Kennedy’s example.